Pivotally mounted high performance print magnet

ABSTRACT

In a high performance print magnet, magnet yokes are independently resiliently mounted on a common support, the yoke is tapered at the pole face to concentrate the flux attracting the armature, and the push rod used to actuate a pivoted print hammer is spring biased to hold the magnet armature against a back stop and prevent the push rod from following the print hammer after the magnet armature seals.

United States Patent [72] Inventors Robert C. Burns Conklin;

John E. Drejza, FAdwell; Do'nlnd F. Manning, Endioott; Richard L. Stark, Johuon City; Donald J. Stiles, Endwell; Joseph E. Wallace; Joseph T. WilsonJIl,

, 126016611, .11 or, 1H. [2]] Appl. No. 887,149 1 [22] I Filed Dec. 22,1969 [45] Patented June 22, 1971 73] Assignee International Business Machines Corporation Armonk, N.Y.

[54] PIVOTALLY MOUNTED HIGH PERFORMANCE PRIN'I'MAGNET 7Claima,5DnwingFigs.

521 11.5.0 101/93, 33s/277,335/193 s11 IIILCI B4lj9/38, B4lj7/84,H0lf7/14 [50] FieldoiSearch l0l/93C,

[56] ReierencesCited UNITED STATES PATENTS 3,241,480 3/1966 Cunningham; 101/93 3,279,362 l0/1966 Helms 101/93 3,282,203 11/1966 Kalbachetal 101/93 3,314,359 4/l96 7 Martin...., 101/93 3,359,921 12/1967 Arnold 101 93 3,490,366 1/1970 Bensonetal.... 101/93 3,504,623 4/1970 Staller 101/93 Primary Examiner-William 8. Penn Attorneys-Hanifin and Jancin and Francis V. Giolma ABSTRACT: In a high performance print magnet, magnet yokes are independently resiliently mounted on a common support, the yoke is'tapered at the pole face to concentrate the flux attracting the armature, and the push rod used to actuate a pivoted print hammer is spring biased to hold the magnet armature against a back stop and prevent the push rod from following the print hammer after the magnet armature seals.

PATENTEUJUNZZIBYI 3585,92?

SHEET 1 [)F 3 ROBERT D. BURNS FlG. 1 JOHN E. DREJZA DoNALD F. MANNING RICHARD L. STARK DONALD J. STILES JOSEPH E WALLACE JOSEPH T. WILSONIII a ATTORNEY PATENTED JUN22 I9?! SHEET 2 OF '3 FIG.

FIG. 4

PIVOTALLY MOUNTED HIGH PERFORMANCE PRINT MAGNET FIELD OF THE INVENTION This invention relates generally to print magnets and print hammer actuators of the electromagnetic type.

DESCRIPTION OF THE PRIOR ART Heretofore, a plurality of print magnets for a high speed printer have been mounted in side-by-side relation on a common support bar by bolts or the like, and temperature-compensating elements have been required in the energizing circuits therefore to compensate for changes in flight time with changing temperature conditions.

SUMMARY OF THE INVENTION Generally stated, it is an object of this invention to provide an improved print magnet for a high speed printer.

More specifically, it is an object of this invention to provide for improving the performance characteristics of the print magnets in a high speed printer so as to assure a rapid print mechanism settle out.

Another object of the invention is to reduce the shock wave transmitted from one print magnet to adjacent print magnets as a result of operation of said one print magnet.

Yet another object of the invention is to reduce the magnetic interaction between adjacent print magnets.

It is also another object of this invention to provide for biasing the push rod which operatively connects the print magnet to the print hammer so as to preload the print magnet armature and prevent the push rod from following the print hammer after the magnet armature seals against the magnet yoke.

Another important object of this invention is to minimize variations in the operating time of a plurality of side-by-side arranged print magnets in a high speed printer.

Yet another important object of this invention is to provide for increasing the cross section of the magnet yoke relative to the armature cross section, and for reducing the cross section of the magnet yoke at the pole face so as to concentrate the magnetic flux, which increases the magnetic force and thereby increases the magnet armature velocity.

Yet another object of the invention is to provide for pivotally mounting a print magnet yoke on a support, and for biasing the print magnet yoke against a stop which provides a support for the armature back stop of the print magnet.

In a preferred form of the invention a print hammer mechanism comprises a print magnet having a magnet yoke with a section having a reduced cross section pole face and having an operating winding thereon for operating a pivoted armature. The armature is connected by a slender push rod to a pivoted print hammer, and the push rod is biased against the armature in the rest position by a spring. The print magnet yoke is pivotally mounted on an L-shaped support, the lower leg of which is secured to a common support bar upon which a plurality of such magnets are mounted. A spring biases the print magnet yoke against the vertical leg of the support and absorbs sufficient energy when the armature is actuated, whereby mechanical shock waves are precluded from upsetting the rest condition of adjacent print magnet annatures and changing their operating times.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawing.

DESCRIPTION OF THE DRAWING In the drawing: FIG. .1 is a schematic view of one type of printer apparatus with which the invention may be used.

FIG. 2 is a side view in elevation showing various elements which form a-basic hammer unit of the prior art,'with the elements illustrated in the operating relation at the time of rest.

FIG. 3 is a view generally similarto FIG. 2 showing a basic hammer unit of the present invention, with the elementsillustrated in the operating relation at the time of rest.

FIG. 4 is a schematic circuit diagram showing a typical operating circuit for the prior art print hammer of FIG. 2, and

.FIG. 5 is an end elevational view of the magnetic shield used with the magnet winding of the present invention.

Referring to the drawing:

FIG. 2 shows in detail one of the plural arrangement of individual hammer units for incorporation into theprinter apparatus of FIG. 1, as described in U.S. Pat. No. 3,241,480, which issued on Mar. 22, 1966, to]. M. Cunningham and is entitled Print Hammer Mechanism and Pressure Control Means in High Speed Printers." As shown therein, one of a plurality of electromagnets 40 is mounted on a support shelf 28, the attachment of the electromagnets being, for example, mounted by fitting the base of the electromagnet yoke 41 in grooves (not shown) in the surface of the shelf 28. The electromagnets 40 each comprise a U-shaped yoke 41 having spaced forward and reverse legs 42 and 43, respectively. An energizing winding 44 is mounted on an inwardly extending core portion 45 of the yoke leg 42. Superimposed on the rear leg 43 of the yoke leg 41 is a metal buffer block 46 and a resilient energy absorber block 47 of a material such as butyl rubber. An armature 48 is pivotally supported by a pin 49 between the legs 42 and 43 by suitable mounting means such as side plates or straps 50 secured to each side of the legs by means of screws 50a. The inwardly facing core extension 45 of yoke leg 42 limits the forward stroke of armature 48. The metal block 46 and the energy absorber block 47 serve as antirebound means which absorb energy from the armature 48 when it is rotating clockwise after rebound of the hammer element 60.

Supported on a similar shelf 29 along the front edge thereof are a plurality of hammer modules represented by the module 51. As shown, each hammer module 51 comprises an L- shaped mounting frame 52 having a horizontal base portion 53 attachable to the underside of shelf 29, and a vertical front portion 54 extending upwardly in front of shelf 29. A plurality of grooves or recesses 55 in the forward section 54 are separated by parallel guide ribs 56. In the hammer module are mounted a subgrouping of individual hammer elements 60, pivotally mounted by a pin 57 to the vertical portion 54 within the recesses 55 between adjacent guide ribs 56. A stop plate 58 is provided to the rear of the hammer 60 for engaging the hammers when a module is removed from the unit assembly. As shown, each hammer element 60 comprises a hub portion 61 which pivots around pin 57. Radiating upwardly from the hub portion 61 is a relatively long striking arm 62 which carries an anvil 63 near the outer extremity thereof. The anvil 63 is preferably made of hardened material such as alloy steel. The striking arm 62 terminates in a spur 64 extending rearwardly from the anvil 63, which terminates in a hook portion 65 extending outwardly beyond the anvil 63. Radiating downwardly from the hub portion 61 if a return arm 66 which engages a stud 67 carried in a biasing spring 59 located within a recess 68 in each hammer groove 55. The arm 62 is preferably relatively thin in relation to its width, and the anvil 63 is relatively massive'in order to locate the center of mass as close as possible to the center of the anvil, which is the center of impact. In addition, by making the spur 64 in line with the anvil 63 and causing it to terminate at a point beyond the anvil, the center of mass is additionally advanced nearer the center of impact. An L-shaped paper guide 69 is mounted on or carried by the hammer module frame 52 by means of pivot arm 70. A spring 71 attached to the underside of frame 52 by screw 72 biases the paper guide 69 in a counterclockwise direction around the pin 70.

modules 51 are connected by connector assemblies or modules 75 mounted in a coplanar array on the upper surface of the middle support shelf 29 and intermediate the hammer modules 51 and electromagnets 40. Each connector module 75 comprises a plurality of push connectors typified by the slender column push connector wire element 82 movably supported within grooves 77 formed in one surface of a connector module block member 76. A cover plate 78 superimposed on the block member 76 coacts therewith to form laterally closed guide or support channels in the connector module 75. To accommodate the connection of various print hammers 60 to the various electromagnets 40 the push connectors 82 may be of two different lengths, each push connector 82 being a slender column. Each connector 82 may comprise a fine wire of a circular cross section dimensioned to assure a loose fit within the channel. The desired looseness of fit is obtained by providing a groove channel 77 which has a square cross section for receiving the wire which is circular. In addition, the block member 76 and cover plate 78 are made of a low friction, high strength plastic material with the wire element 82 formed of a high compressive strength metal such as carbon steel, music wire, or the like. A separate retainer plate 81 is provided for each connector module 75 so that individual replacement and assembly of the connector modules may be made.

When the winding 44 of electromagnet 40 is energized, armature 48 is attracted towards the core extension 45 and rotates counterclockwise around pivot 49. Preferably, the energization of the winding 44 occurs with a relatively short high-amplitude pulse which attracts the armature 48 at a rate which increases acceleration of its motion until such time as it is arrested abruptly by impact with the end of the core extension 45. During the acceleration of the armature 48 around its pivot 49 the push wire 82 is being displaced laterally towards the paper 13. Hammer element 60 at the same time is rotated in a counterclockwise direction around its pivot 57 against the bias of spring 59. Because the push connector 82 and hammer element 60 are in contact at the time that the winding 44 is energized the push wire 82 and hammer element 60 are accelerated by a pushing motion rather than a striking motion. Thus, there is no impact on the wire element 82 or hammer element 60 which would tend to dissipate energy and damage the operating parts. At the instant that the armature 48 is arrested by contacting the core extension 45, the end of the armature 48 is travelling at its maximum velocity. The velocity of the push connector 82 and the print hammer element 60 will also have reached its maximum level at the same instant. The momentum of the push connector 82 and the hammer at the instant when the armature 48 has been arrested, is of sufficient magnitude that both the push connector 82 and the hammer element 60 continues to move towards the point of impact with the paper 13 and type characters. The print hammer element hook 65 comes in contact with the compres- I sion control pad 92 on the impression control bar 90 about the same time the anvil 63 impacts the paper and the ink ribbon 14 against a type character on a type element 11 moving on the stationary frame 12. The return arm 66 of the print hammer element 60 will have compressed the return spring 59 in the frame 52. The momentum on rebound of the hammer 62 is sufficiently great that it picks up the push wire connector 82 in case the two have become separated and moves it backward to the point where it comes in contact with the upper extremity of the armature 48.

In the described embodiment of the prior invention shown in FIG. 2 the winding 44 will have been deenergized before the push connector 82 recontacts the armature 48 on its return stroke. The armature 48, however, will be retained in its forward position because of residual magnetism in the leg 42, including core extension 45 and in the annature 48. The residual magnetism in this case serves as a desirable means for damping the print hammer element 60. and the push connector 82 afterrebound. In addition, on rebound the push connector 82, when it contacts the armature 48, breaks it away from its position against the core extension 45 and causes it to strike against the buffer block 46, where the remaining portion of the kinetic energy in the print hammer element 60 and the push connector 82 and armature 48 is dissipated in the resilient block 47. The print hammer element 60 is then in a position for reenergization on a subsequent operation.

Referring to FIG. 3 of the drawing, it will be seen that the arrangement of the present invention is generally similar to that described for the prior art structure of FIG. 2. As shown, a plurality of print hammers represented by the hammer 160 are pivotally mounted on the front side of a print medium 113. Print hammers 160 are arranged to be uniformly spaced so that one hammer element occupies each of a plurality of print positions along the print line and the hammers 160 are aligned in a single row parallel to the print line. Each print hammer 160 is part of an individual hammer unit which comprises, in addition, an electromagnet 140 with an armature 148, a push connector element 182 connecting the armature 148 and hammer 160, and bias spring 159, which maintains the hammers 160 out of contact with the paper 113 when the electromagnet 140 is deenergized. Each hammer 160 is individually operable to impact a pivotal type lever 111a carried by a type carrier moving along a rail 112a of a frame 112, against a ribbon 114, paper 113, and platen 123 and the operation of the various hammers occur selectively at random positions along the print line in accordance with instructions from a suitable control means (not shown) which comprises a type tracking device and a coacting storage device which indicates the data to be printed. Further details of a suitable control system may be more fully understood by reference to US. Pat. No. 2,993,437 which issued on July 25, 1961, to F. M. Demer et al.

As shown, each electromagnet 140 comprises a generally U- shaped magnet yoke 141 having spaced forward and reverse legs 142 and 143, respectively, connected by means of a screw 140a. An energizing winding 144 is mounted on an inwardly extending core portion 145 of the yoke leg 142. Instead of utilizing the metal buffer block 46 and resilient energy absorber block 47 of P16. 2, the leg 143 is provided with an adjustable stop screw 146 having a resilient energy absorbing pad 147 of a plastic material such as polyurethane. The armature 148 is pivotally supported by a pin 149 between the legs 142 and 143 by suitable mounting means such as the side plates or straps 150 secured on opposite sides of the leg 143 by screws 150a. The stop screw 146 and pad 147 serve as antirebound means, which absorbs energy from the armature 148 when it is rotating clockwise after rebound of the hammer element 160.

Instead of being secured directly to the shelf or support bar 128, as described in connection with the structure of FIG. 2, the yoke 141 of the electromagnet 140 is secured to the support 128 by means of an L-shaped support member 139 having a horizontal leg portion 139a and a vertical leg portion 13%. The horizontal leg portion 139a is secured to the support bar 128 by means of screws 1280. A pivot pin 138 located in openings 137 in the side plates 150 and passing through the horizontal leg portion 139a provides a pivotal connection between the electromagnet 140 and the support member 139. A spring positioned in recess 133 in the horizontal leg 139a and the lower end of the leg 141, respectively, biases the electromagnet in a clockwise direction, so that the leg portion 143 rests against the vertical leg portion 13% of the support member 139 in the normal rest position. This pivotal connection provides a resilient energy absorbing connection between the electromagnet 140 and the support plate 128, which allows the magnet yoke 141 to move first counterclockwise, then clockwise relative to the mounting base or shelf 128 lduring and after the time the armature 148 impacts the core extension as the seal of the magnet armature 148 occurs, in response to energization of winding 144, which causes the armature 148 to rotate about pivot 149 and contact core extension 145.1n allowing the yoke 141 of electromagnet 140 to move, the pivotal connection permits the energy of the armature 148 to be redistributed into the combined mass of the armature 148 and the yoke 141, where it is later absorbed by the spring 135, which also acts to return the system to its initial position with the stored energy. In allowing the above action to develop, the energy that can get through the spring 135 or pivot connection 149 to the support member 139 and the support bar 128, is considerably reduced. The design shown reduced the variation in print hammer 160 flight time due to this effect, to less than l0 microseconds, when four adjacent electromagnets 140 were fired under the worst case relative timing conditions. This compares with corresponding time variations in adjacent electromagnets 40 that were measured to be as high as 70 microseconds less than the normal flight time with the print hammer mechanism of the prior art as illustrated in FIG. 2.

The reduction in stress levels in the system due to this action causes timing variations due to wear (the residual pole face and pivot) to be reduced. Because the vibration transmitted to the mounting plate or shelf 128 through the mounting screws is considerably reduced, the tendency for the screws to loosen or change position and allow further timing adjustments to change, is considerably reduced. The isolating mechanism also acts in the reverse direction to prevent any vibrations in the mounting plate or shelf 128 from disturbing the armature 148. A spring 135 having a spring rate of 180 lbs. per inch has been found most effective with the electromagnet 140 having a mass on the order of 4.19 l0(lb sec lin). The electromagnet yoke 141 is biased with a force of approximately 7.5 lbs. in the rest position.

Studies of prior art magnet structures revealed that operation of one magnet caused magnetic flux to develop in a neighboring magnet which was of a sufficient magnitude to cause variations (as much as 50 microseconds) in the operating or flight time of these magnets. The present design eliminates or minimizes this problem by using an iron shield in the form of a U-shaped spring steel clip 114a, as shown in FIG. 5, and which fits around the operating winding and has inturned end portions 144b and 1440, which terminate in close proximity to the leg portion 145 of the magnet yoke 141. This shield acts to contain any leakage flux so that it has a considerably reduced effect (less than microseconds) on any adjacent magnet.

The push rod 182 is provided with a control spring 184 located in an opening 174 in the connector module 175. The spring 184 is a helical compression spring which bears against the edge of the opening 174 and against a collar 167 secured to the push rod 182. The spring 184 biases the push rod 182 against the magnet armature 148 and with spring 159 holds the armature 148 against the back stop pad 147 in the rest position. A control spring 184 having a spring rate of 1.2 lbs. per inch has been found most effective, and biases the armature to its rest position with a force of 0.1 lbs. The hammer spring 159 has a spring rate of 0.77 lbs. per inch and provides a preload force of 0. l 8 lbs. to the armature 148 in its rest position. The control spring 184 keeps the push rod 182 in contact with the magnet armature 148 while the magnet armature 148 is in motion, and prevents it from following the hammer 160 after the armature 148 impacts or seals against the core portion 145 on which the operating winding 144 is mounted. This reduces type nipping by the print hammers 160 as the type levers 1110 move past the hammers 160, and the more predictable position of the push rod 182 improves the repeatability of the print unit settle out. This provides a greater uniformity in the recycling time of the print magnet mechanism.

According to the present invention, the magnetic efficiency of the electromagnet 140 has been increased by using a tapered yoke portion 145a adjacent the face of the core leg 145 on which the operating winding 144 is located. By making the core leg 145 generally of greater cross section than the cross section of the armature 148 and then tapering the core leg 145 adjacent the armature, the amount of flux in the core is increased and is concentrated at the pole face where it is most effective. By making the core leg 145 longer, a larger size of wire can be utilized, thus, reducing the resistance of the winding .and hence, the heating. Because of the increased length of the core leg 145, heating thereof tends to reduce the air gap due to thermal expansion between the core leg 145 and the armature 148 in its rest position against the pad 147. At the same time, support 139, on which the electromagnet is pivotally mounted, provides a stop for leg portion 143 allowing the biasing of electromagnet 140 clockwise by spring 135. Thermal expansion due to an increase in the operating temperature of the assembly results in the stop 146 urging the armature 148 counterclockwise towards the core leg 145, thus, further reducing the air gap between the core leg and the armature 148, and further decreasing the seal time for the armature to contact the core leg 145. A reduction in the air gap between the armature 148 and the core leg 145 by reason of expansion of the core leg 145 reduces the air gap and tends to accelerate the armature earlier, thus, offsetting a reduction in the current in the operating winding 144 due to the increased resistance because of the increased temperature of the winding. At the same time a reduction in the air gap between the armature 148 and the core leg 145, by reason of movement of the back stop 147, tends to advance the push rod 182, and preposition the print hammer closer to the type lever 111a so that it has less distance to move in order to print. This results in consistent flight time even though the current in winding 144 has been reduced.

The improved design of the present invention not only reduces variation in flight time of the print hammer because of a reduction in mechanical shock wave effect on the print magnet armatures, but the effect of temperature changes on the flight time are minimized over the complete range. Because of the changes in structure including the physical changes in the design of the electromagnet as well as the method of mounting it, it is now possible to increase the repetition rate of operating the electromagnet to double'the operating rate of the magnet of the prior art so as to have the capability of printing at 2,200 lines per minute instead of 1,100 lines per minute, without requiring the use of a thermal-compensating element, such as the thermistor 44r which was heretofore required in the circuit of the operating winding 44 and the driver 44D as shown in FIG. 4.

. While the invention has been particularly shown and described with reference to a preferred embodiment thereof it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

What we claim is:

1. ln a printer apparatus having a moving type element and a pivoted print hammer mechanism for impacting said type element and a print medium,

an electromagnet actuator comprising a magnetizable core member having an armature pivotally mounted thereon and having an operating winding,

a slender column push rod operatively connecting said armature and said print hammer,

support means pivotally supporting the electromagnet actuator core member, and

resilient means biasing the core member to a predetermined position relative to said support means.

2. The invention as defined in claim 1 characterized by a pair of side plates secured to said core member, said side plates carrying one pivot for said armature and another pivot connecting said core member to said support means.

3. The invention as defined in claim 2 characterized by said core member comprising a generally U-shaped structure having two legs with said armature mounted therebetween and having said operating winding on one leg and a back stop for said armature on the other leg.

4. The invention as defined in claim 3 characterized by said support means comprising an L-shaped member having a lower leg disposed to be secured to a common support bar for a plurality of electromagnet actuators and an upright leg disposed to engage said other core leg.

tion from said one leg, said core projection having a pole face adjacent said armature with a tapered end portion which concentrates the magnetic flux at said pole face.

7. The invention as defined in claim 6 characterized by said operating winding having a magnetic shield of spring steel with end portions inturned in close relation with the core projection. 

1. In a printer apparatus having a moving type element and a pivoted print hammer mechanism for impacting said type element and a print medium, an electromagnet actuator comprising a magnetizable core member having an armature pivotally mounted thereon and having an operating winding, a slender column push rod operatively connecting said armature and said print hammer, support means pivotally supporting the electromagnet actuator core member, and resilient means biasing the core member to a predetermined position relative to said support means.
 2. The invention as defined in claim 1 characterized by a pair of side plates secured to said core member, said side plates carrying one pivot for said armature and another pivot connecting said core member to said support means.
 3. The invention as defined in claim 2 characterized by said core member comprising a generally U-shaped structure having two legs with said armature mounted therebetween and having said operating winding on one leg and a back stop for said armature on the other leg.
 4. The invention as defined in claim 3 characterized by said support means comprising an L-shaped member having a lower leg disposed to be secured to a common support bar for a plurality of electromagnet actuators and an upright leg disposed to engage said other core leg.
 5. The invention as defined in claim 4 characterized by means on said push rod biasing said push rod and said armature to a rest position against said back stop.
 6. The invention as defined in claim 5 characterized by said operating winding being located on a horizontal core projection from said one leg, said core projection having a pole face adjacent said armature with a tapered end portion which concentrates the magnetic flux at said pole face.
 7. The invention as defined in claim 6 characterized by said operating winding having a magnetic shield of spring steel with end portions inturned in close relation with the core projection. 